function ret=yz_rotation_form(alpha,theta,beta)
 a11=exp(1i*(alpha/2+beta/2))*cos(theta/2);
 a12=exp(1i*(alpha/2-beta/2))*sin(theta/2);
 a21=-exp(1i*(-alpha/2+beta/2))*sin(theta/2);
 a22=exp(-1i*(alpha/2+beta/2))*cos(theta/2);
 ret=[a11 a12;a21 a22];
endfunction
